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Convertin 50i to 50p (100i)

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Marcello MazzilliConvertin 50i to 50p (100i)
by on Oct 10, 2009 at 12:11:03 pm

I'm sorry.. this could not be the correct forum.. but didn't really find one that was good...

I am trying to convert 50i footage WITH NO INTERPOLATION ALGORITHM to 100i footage (or 60i to 120i). The idea is to use the same algorithm that LCD TV sets so... Once I get the 100i I'll use normal interpolation codecs to create 50p.

Let's say you have 50i footage. This contains information at half resolution for every 1/50th of time.
these informations are combined interlacing lines 2 by 2. So every frame (actually 2 fields) is made with upper (U) and lower (L) fields combined together... Like this...

1U1L, 2U2L, 3U3L, etc...

This decision of combining the frames 2 by 2 has a reason that comes from old CRT TVs technology (that use to "draw" lines with an electron pen). New LCDs work differently. They need to have full frames to display so if they have 25p footage they just display 25 frames, but if they have 50i footage they create 50p footage using this algorithm..

1U1L, 1L2U, 2U2L, 2L3U, 3U3L, etc..

This algorithm is very simple (and fast... no work is actually done on data.. just data relative to fields is moved around.

The problem is that I cannot find a software that uses this algorithm. This because software do much more... I could change 50i to any other timing like 67i, 98i, 103i etc... and AfterFX would do very good interpolation. But... it would be very slow and.. it is interpolation....

If the timing is exactly DOUBLE you can use "my" algorihm. This would not make much sense on a CRT 100i TV (if you still find it).. but would be very good if after you interpolate the two fields to one progressive frame.

So.. concluding.... If you shoot in 25p is better than to interpolate 50i.. but if you shoot in 50i it should be much better to interpolate at 50p than to do it at 25p.

Does somebody know a software that will let me work on raw data in the video file (whatever format, wrapper, codec.. is just data!) ?

siRoma di Marcello Mazzilli
Corporate video productions in Italy
http://www.siroma.com


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Chris WrightRe: Convertin 50i to 50p (100i)
by on Oct 10, 2009 at 7:59:10 pm

Your whole premise lies on the fact that the TV gimic of 120 hz, 300 hz etc. makes (example. football games look better.) This is just a gimic. The real and only method that counts, besides a good uprezing, is the adaptive motion algorithm that reduces judder swish pans in DVD's, which in the newer models, you can turn on and off. Our eyes can only see up to 60-70hz or 60-70fps. Try outputting a 100 fps file and see if you can see a difference. Now if you're still a go, read on...

I think you mean 25i which is 50 fields/sec. not 50i. Now if you want to convert the 50 fields/sec to 50 frames/sec render fields off, just interpret fields on, and drop the 25i into a 50fps comp and AE will automatically do a no interpolation stretch and turn each field into a frame. Its a good method for motion tracking and rotoscoping, but not for greenscreening.

You said,
"So.. concluding.... If you shoot in 25p is better than to interpolate 50i.. but if you shoot in 50i it should be much better to interpolate at 50p than to do it at 25p."


25p is better than interpolate 50i is a backwards statement. If according to your premise you want smoothness, you would actually say, ""25i is better than 25p because you have smoother motion and more data.


You are right though about interpolating at 50p is better than than 25p. to get to 100 fields/sec... if that were usefull or neccessary...

http://technicolorsoftware.hostzi.com/


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Marcello MazzilliRe: Convertin 50i to 50p (100i)
by on Oct 10, 2009 at 10:24:07 pm

No sorry.. I think there could have been some misunderstanding here.My fault maybe.. I'm not english language

1) Interlaced PAL (that is 25 fps) is usually written 50i (and not 25i) as interlaced NTSC is written 60i (and not 30i).

2) When I say 25p is better than 50i.. i mean... "shooting in 25p is better than shooting in 50i and interpolating afterwards". 50 K$ cameras shoot also 1080/50p and that's even better. My camera shoots only 720/50p but not 1080/50p so I have to shoot either 1080/25p or 720/50p or 1080/50i. Sometimes (for many reasons ) I choose 50i and then sometimes I interpolate to 25p. I would like to convert (not interpolate!) with the method I described to 100i (not 100 fps but 50 fps!) and then interpolate to 50p to get better slow motion (but not better frame quality) than 25p. Hope is clear!

3) I know there are nice interpolating algorithms around.. I just want to avoid algorithm if I need EXACTLY 50% slow motion. It's better and faster to use (if I find how) the method described

Anyway.. thanks for interest

siRoma di Marcello Mazzilli
Corporate video productions in Italy
http://www.siroma.com


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Chris WrightRe: Convertin 50i to 50p (100i)
by on Oct 10, 2009 at 11:41:51 pm

this tutorial will show you how you can slow your footage down to 50% without interpolating the frames between.

http://maltaannon.com/articles/after-effects/slow-motion/

http://technicolorsoftware.hostzi.com/


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Marcello MazzilliRe: Convertin 50i to 50p (100i)
by on Oct 11, 2009 at 8:53:03 am

Seems to work.. but I'm not sure it's doing what I was thinking. I have to test it. As far as I can see he keeps fields in the same frame and just creates a half res frame every 1/50th of a sec.

siRoma di Marcello Mazzilli
Corporate video productions in Italy
http://www.siroma.com


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